The lowest-lying glueballs are investigated in lattice QCD using N f = 2 clover Wilson fermion on anisotropic lattices. We simulate at two different and relatively heavy quark masses, corresponding to physical pion mass of mπ ∼ 938 MeV and 650 MeV. The quark mass dependence of the glueball masses have not been investigated in the present study. Only the gluonic operators built from Wilson loops are utilized in calculating the corresponding correlation functions. In the tensor channel, we obtain the ground state mass to be 2.363(39) GeV and 2.384(67) GeV at mπ ∼ 938 MeV and 650 MeV, respectively. In the pseudoscalar channel, when using the gluonic operator whose continuum limit has the form of ijk T rBiDjB k , we obtain the ground state mass to be 2.573(55) GeV and 2.585(65) GeV at the two pion masses. These results are compatible with the corresponding results in the quenched approximation. In contrast, if we use the topological charge density as field operators for the pseudoscalar, the masses of the lowest state are much lighter (around 1GeV) and compatible with the expected masses of the flavor singlet qq meson. This indicates that the operator ijk T rBiDjB k and the topological charge density couple rather differently to the glueball states and qq mesons. The observation of the light flavor singlet pseudoscalar meson can be viewed as the manifestation of effects of dynamical quarks. In the scalar channel, the ground state masses extracted from the correlation functions of gluonic operators are determined to be around 1.4-1.5 GeV, which is close to the ground state masses from the correlation functions of the quark bilinear operators. In all cases, the mixing between glueballs and conventional mesons remains to be further clarified in the future.

We propose a strategy to access the qq component of the ρ resonance in lattice QCD. Through a mixed action formalism (overlap valence on domain wall sea), the energy of the qq component is derived at different valence quark masses, and shows a linear dependence on m 2 π . The slope is determined to be c1 = 0.505(3) GeV −1 , from which the valence πρ sigma term is extracted to be σ (val) πρ = 9.82(6) MeV using the Feynman-Hellman theorem. At the physical pion mass, the mass of the qq component is interpolated to be mρ = 775.9 ± 6.0 ± 1.8 MeV, which is close to the ρ resonance mass. We also obtain the leptonic decay constant of the qq component to be f ρ − = 208.5 ± 5.5 ± 0.9 MeV, which can be compared with the experimental value f exp ρ ≈ 221 MeV through the relation f exp ρ = Zρf ρ ± with Zρ ≈ 1.13 being the on-shell wavefunction renormalization of ρ owing to the ρ − π interaction. We emphasize that mρ and fρ of the qq component, which are obtained for the first time from QCD, can be taken as the input parameters of ρ in effective field theory studies where ρ acts as a fundamental degree of freedom.

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